Radiointerference preventer



T. M. LlBBY.

RADIOINTERFERENCE PREVENTER.

APPLlCATlON FILED OCT-21,1919.

1 365326, Patented Jan. 18, 1921.

WITNESSES m mvron UNITED STATES PATENT OFFICE.

TYNG M. LIBBY. OF TACOMA, WASHINGTON, ASSIGNOR TO HENRY G. CORDES, OF

BBEMERTON, WASHINGTON.

RADIOINTERFERENCE PBEVENTER.

Specification of Letters Patent. Patented J an.- 18, 1921,

Application filed October 21, 1919. Serial No. 332,200.

'1 '0 all whom it may concern Be it known that I, TYNG M. LIBBY, a citizen of the United States, residing at Ta coma, in the county of Pierce and State of \Vashingtou, have invented a new and useful lmprovcment in Radiointerferencelrcrenters.

My invention relates to an im movement in means for counteracting the e cut of interfering signals in a receiving oscillatory circuit of a receiving radio signal system when the interfering signals are caused by a transmitting station which emits 'feebly damped waves, constant amplitude waves or waves in which the rate of change of amplitude is comparatively small as in radio tele hony. -The preventive means are most e ective when the interfering wave is a constant frequency sinoidal wave differing considerably in length from the wave of the signal selected for reception.

The object of my inventiolris to provide means whereby interference can be counteracted in an oscillatory circuit withoutchangin the resonant frequency of the circuit.

This object is attained by connecting two reactances in parallel and adjusting one of them for zero value at the resonant frequency of the oscillatory circuit in which the interfering signal current flows. The parallel reactanccs are then connected in series with the oscillatory .circuit and the parallel reactances in series with each other are ad justed for zero value at the frequency of the interfering signal current.

The procedure heretofore has been to connect the parallel reactances in series with the oscillatory circuit, to adjust the parallel reactances in series with each other for zero value at the frequency of the interfering current and then to adjust the reactance of the oscillatory circuit so that. the reactance of the oscillatory circuit in series with the parallel reactances will be zero at the frerepresents diagrammatically a complete radio signal receiving system of the present frequency upon the antenna circuit the re-- actance of inductance 10 and condenser 11 in series is made equal to the reactance of the antenna circuit at resonant frequency and then switch 1 is thrown to the left. The inductance 12 is then adjusted until the reactance of inductance 10, condenser 11 and inductance 12 in series is zero at the frequency of the interfering impressed electromotive force. In Fig. 1 it is assumed that the frequency of the interfering electromotive force is less than the frequency of the impressed electromotive force due to the signal selected for reception.

when the interfering current in the antenna circuit is a minimum.

For convenience let the reactance of the antenna circuit be represented by X when switch 1 is thrown to the, right. Let the reactance of inductance 10 and condenser 11 in series he represented by Y and let the reactance of inductance 12 be represented by Z. Then both X and Y are zero at the frequency of the waves of the signal selected for reception and Y plus Z equals zero at the frequency of the interfering waves.

The word frequency as applied to waves refers throughout this specification to the quantity which is inversely propor tional to wavelength or length of the waves.

The total reactance of Xin series with Y and Z in parallel will be represented by U which is expressed mathematically by the equation,

from which it is seen that U is zero when both X and Y are zero. For every value of Parallel resoname is attained in the circuit 1011-12 Z thereis a second fre uency at which U e uals zero and a third equency at which equals infimty.

The parallel reactances Y and Z .in series when connected in series with X will be desated the parallel resonance circuit. The

- circuit 1l--12'is the parallel resonance circuit in Fig. 1. The reactance of the series resonance circuit is'either X when swltch thrown to the r' ht ,or IIwhen switch 1 1s 7 thrown to the le The parallel resonance .circuit constitutes an infinite reactanc'e to current through X having the frequency at which parallel resonance takes place.

reactance X an the reactance of the secondary oscillatory circuit aregraduated in the' usual manner for wavelength at a given coupling. The reactance is (graduated for wavelengths and before intro ucing the arallel reactance the reactance Y is adusted to the same wavelength as X. The

reactance Z can alsobe graduated in arbi-,

trary units sothat for every value of reactance .Y there is a set of values of Z which can be tabulated for reference. Reception of the selected signal is not interrupted while Z isbeing adjusted for zero 'reactance' in the. parallel resonance circuit i :at the frequency of the interfering waves.

. the circuit.

Fig. 2 lllustrates a modification of the parallel resonance circuit of Fi 1;. The

condenser .13 is substituted for inductance 12 ofFig. 1 so that the parallel resonance circuit 10-11-13 may be adjusted for zero reactance at a frequency which is greater than theresonant frequency of the antenna circuit when switch 1; is closed. In Fig. 2. *"the antenna circuit is not broken while the parallel reactances are being introduced into In. Fi 1 the reactance Z is positive while in F1g.-2 the reactanc'e Z is -negative When swltch 1 is closed .actance of the antenna circuit is X.

the. re-

Fig. 3illustrates another modification of it the arallel resonance circuit of 1. A

con ense'r 13 is placed in series wit induc 'ta-nce'12 so that the reactance of the parallel resonance circuit; 10.-11+13-'-1-2 can be made zero at anyfrequency. The arallel interferis opened depending upon whether the frequency or wavelength of the interfering wave is lmown as in duplex signaling or is not known.

The resistance of a parallel resonance circuit should be reduced to a minimum since the amplitude of the interfering alternating current flowing in the antenna circuit is proportional to the ohmic resistance in the parallel resonance circuit and the amplitude is also inversely proportional to the product YZ when the ohmic resistance is negligible compared to both reactance Y and to reactance Z. In order to reduce the resistance of reactances Y and Z in series to a minimum the parallel resonance circuit should consist of a continuous conductor between the dielectrics of the condensers and the condenser dielectric should be air. The conductorshould preferably have large surface area per unit length. he inductailces-can be made in the form of a helix and their value can be varied by varying the length of the helical coil in the direction of its axis. The capacitance of the condensers can be variedin the usual manner by moving one armature or pole oflthe condenser with respect to the other armature or pole.

4 is similar to Fig. 3 except that provlsion is made to counteract interference from two interfering stations. Interference from the first station is counteracted by the parallel resonance circuit 10-11-13-12 with switch 1 .open and switch 18v closed which is equivalent to Fig. 3. When it becomes necessary to counteract interference from a second station the reactance of inductance 14 and condenser 15 in series is made zero at the resonant frequency of the antenna circuit. Switch 18 is then opened and either or both inductances 16 and condenser 17 are adjusted for zero reactance in the second parallel resonance" circuit ;1115-17-- 16 at the frequency of thewaves emitted by the second interfering station. Anyigiumber of pairs of parallel reactances may 'thus be connected in series with an oscillatory circuit without changing its resonant frequency.

The present state of the art with respect to preventing interference by means of a 'arallel resonance cirtuit is described in the ureauof Standards Circular No. 74, page 39 et seq. In this publication it is noted that by making the capacitance in Y equal to the capacitance in X and making the "inductance in Y equalto the inductance in X'that reactance Z can be varied without changing the frequency at which U is zero. .-This is [special case of my arrangeinent' and "is very limited in its application Itflm'aybacompared to limiting the capaci- '-l remna'nee may be adjusted or zero J tance ofgfthe secondary oscillate I-circriit to at :thefrequency :of the il current either .before;qi: af ter switch 1 the value'of-the'caplwitance of e antenna M improvement consists in making the pro uct of capacitance and inductance in Y equal to the product of capacitance and inductance in which allows parallel reactances to be built in a compact form, properl graduated and introduced into any oscil 'atory circuit without changing the resonant frequency of the circuit provided the pgoducts of capacitance and inductance in and Y can be made equal. Reactances Y and Z can be varied by changing either capacitance or inductance. The current in the I parallel resonance circuit is increased as the ratio of inductance to capacitance in Y is 1. The combination of two parallel reactances in series with an oscillato circuit; the first of said reactances being a justed to zero value at the resonant frequenc of said circuit and having inductance di ering' in value from the inductance of said circuit, and, both of said reactances constituting an infinite reactance in series with said circuit for current in said circuit having a frequency differing from said resonant frequency.

2. he combination of three reactances in pa allel, the products of capacitance and inductance of the first and second of said reactances being equal, the capa'citances forming. part of said first and second reactances being unequal, thethird of said reactances having a single path for current and means for impressing electromotive forces of two frequencies in said first reactance.

3. A plurality of pairs of parallel reactances in series with an oscillatory circuit,

one of each pair of said reactances bein zero at the resonant frequency of sai circuit.

4'. The method of introducin parallel reactances in series with an oscil atorycircuit in'which current is flowing without interrupting the flow of current in said circuit and without changing the resonant frequency of said circuit which consists in adjusting one of the parallel reactances for zero value at the resonant frequency of an oscillatory circuit and then introducing said parallel reactances in series with said oscil-.

latory circuit.

5. The method of sup ress'ing an alternating current in an oscil atory circuit which consists in adjusting one of two parallelre- X Y and z are con actances for zero value at the resonant frequency of an oscillatory circuit, introducin said parallel reactances in series with sai oscillatory circuit and adjusting the second of said parallel reactances for parallel resonance at the frequency of the alternating current to be suppressed in said oscillatory I circuit. 1

6. The method of suppressing an alternating current in an oscillatory circuit which consists in adjusting a reactance Y of twoparallel reactances and Z for zero value at the resonant frequency of an oscillatory circuit, adjusting said reactance Z until said reactances Y plus Z become zero at the frequency of the alternating current to be suppressed in said oscillatory circuit and introducing said parallel reactances' in series with said oscillator; circuit.

7. A radio requency alternating current circuit comprising a plurality of parallel resonance circuits, each 'of said circuits comprising two reactances, one reactance of each parallel resonance circuit being zero at a resonant frequency of said alternating current circuit.

8. An oscillatory circuit comprising a plurality of pairs of parallel reactances, one of each pairof said reactances being zero at a resonant frequency of saidcircuit and each of said pairs constituting an nfinite reactance to current in said circuit havin a frequency difiering from said resonant quemz.

9. radio frequency alternating current circuit comprising two parallel reactances, the first of said reactances being adjusted to zero value at a resonant frequenc circuit and having inductance d1 eiing 111 value from the inductance of said circuit and both of said reactances constituting an infinite reactance for current having a frequency differing from said resonant frequency.

10. An oscillatory circuit in combination with a parallel resonance circuit comprising two reactances, one of said reactances being zero at'a resonant frequenc of said oscillato circuit and havin imi uctive reactance di ering from the in uctive reactance of said oscillatory circuit at said resonant frequenc v 11. n combination with a radio frequency current aerial conductor a plurality of parallel resonance circuits, each of said circuits comprising parallel reactances, one parallel reactance of each of said circuits being zero at a resonant frequency of a circuit comprising said conductor.

12. An alternatin current circuit having positive and negative components of reactance in combination with means for suppressing current insaid circuit; said means comprising zero reactance at a resonant frequency of said circuit and a parallel resoof said nance circuit which constitutes a large impedance to current in said alternating current circuit; said zero reactance and said parallel resonance circuit having reactance in common; and, said zero reactance having components differing in value from the components of reactance of said alternating current circuit at said resonant frequency.

13. Means for suppressing current in a radio aerial circuit comprislng a zero reactance at a resonant frequency of said circuit and a parallel resonance circuit which constitutes a large impedance in said radio aerial circuit to current having a frequency at which resonance takes place in'said parallel resonance circuit; said zero reactance having components diflering in value from the components of reactance of said radio aerial circuit at said resonant frequency.

14. Means for suppressing current of an undesired frequency in a radio aerial circuit comprising a zero reactance, a parallel resonance circuit which constitutes a large impedance in said aerial circuit to current having said undesired frequency and means for keeping said zero reactance constant while reactance comprised by said parallel resonance circuit isvaried; said zero reactance having components differing in value from the components of reactance of: said radio aerial circuit. 15. A plurality of means for suppressing alternating current in combination with an alternating current circuit, each of said plurality comprising a parallel resonance circuit and a zero reactance at a resonant frequency of said alternating current circuit; each of said zero reactances having components differing in value from the components of reactance of said alternating current circuit at said resonant frequency.

This specification signed and witnessed on this 6th day of October, 1919.

TYNG M. LIBBY.

\Vitnesses H. J. GIRLENS, ALICE GIRLENS. 

